System and Method for Modulation and Coding Scheme Adaptation and Power Control in a Relay Network

ABSTRACT

A method for determining a Modulation and Coding Scheme (MCS) and power control includes determining an error rate of a communication channel between the UA and at least one of the base station and the RN. When the error rate is below a first threshold, the method includes at least one of increasing the MCS, and reducing a transmission power of the UA. When the error rate is above a second threshold, the method includes at least one of decreasing the MCS, and increasing a transmission power of the UA.

CROSS REFERENCE

This application is a continuation of U.S. application Ser. No.13/389,791 filed Oct. 26, 2012 by Rose Hu, et al. entitled, “System andMethod for Modulation and Coding Scheme Adaptation and Power Control ina Relay Network” (Atty. Docket No. 36019-1-US-PCT—4214-31905), which isa filing under 35 U.S.C. 371 of International Application No.PCT/US2010/045337 filed Aug. 12, 2010 by Rose Hu, et al. entitled,“System and Method for Modulation and Coding Scheme Adaptation and PowerControl in a Relay Network” (Atty. Docket No.36019-1-WO-PCT—4214-31901), which claims priority to U.S. ProvisionalApplication No. 61/233,436 filed Aug. 12, 2009 by Rose Hu, et al.entitled, “System and Method for Modulation and Coding Scheme Adaptationand Power Control in a Relay Network” (Atty. Docket No.36019-1-US-PRV—4214-31900), all of which are incorporated by referenceherein as if reproduced in their entirety.

BACKGROUND

The present invention relates generally to data transmission incommunication systems and more specifically to systems and methods forassociation and uplink adaptation and power control in a relay network.

As used herein, the terms “user agent” and “UA” can refer to wirelessdevices such as mobile telephones, personal digital assistants, handheldor laptop computers, and similar devices or other User Equipment (“UE”)that have telecommunications capabilities. In some embodiments, a UA mayrefer to a mobile, wireless device. The term “UA” may also refer todevices that have similar capabilities but that are not generallytransportable, such as desktop computers, set-top boxes, or networknodes. Throughout the present disclosure the term “UA” is equivalent tothe term “UE”.

In traditional wireless telecommunications systems, transmissionequipment in a base station or other network node transmits signalsthroughout a geographical region known as a cell. As technology hasevolved, more advanced equipment has been introduced that can provideservices that were not possible previously. This advanced equipmentmight include, for example, an evolved universal terrestrial radioaccess network (E-UTRAN) node B (eNB) rather than a base station orother systems and devices that are more highly evolved than theequivalent equipment in a traditional wireless telecommunicationssystem. Such advanced or next generation equipment may be referred toherein as long-term evolution (LTE) equipment, and a packet-basednetwork that uses such equipment can be referred to as an evolved packetsystem (EPS). Additional improvements to LTE systems and equipment willeventually result in an LTE advanced (LTE-A) system. As used herein, thephrase “base station” will refer to any component, such as a traditionalbase station or an LTE or LTE-A base station (including eNBs), that canprovide a UA with access to other components in a telecommunicationssystem.

In mobile communication systems such as the E-UTRAN, a base stationprovides radio access to one or more UAs. The base station comprises apacket scheduler for dynamically scheduling downlink traffic data packettransmissions and granting resources for uplink traffic data packettransmission for all the UAs communicating with the base station. Thefunctions of the scheduler include, among others, dividing the availableair interface capacity between UAs, deciding the transport channel to beused for each UA's packet data transmissions, and monitoring packetallocation and over-the-air resource utilization. The schedulerdynamically allocates resources for Physical Downlink Shared CHannel(PDSCH) and grants resources for Physical Uplink Shared CHannel (PUSCH)data transmissions, and sends scheduling information to the UAs througha control channel.

To facilitate communications, a plurality of different communicationchannels are established between a base station and a UA including,among other channels, a Physical Downlink Control Channel (PDCCH). Asthe label implies, the PDCCH is a channel that allows the base stationto control a UA during downlink data communications. To this end, thePDCCH is used to transmit scheduling or control data packets referred toas Downlink Control Information (DCI) packets to the UA to indicatescheduling to be used by the UA to receive downlink communicationtraffic packets or transmit uplink communication traffic packets orspecific instructions to the UA (e.g. power control commands, an orderto perform a random access procedure, or a semi-persistent schedulingactivation or deactivation). A separate DCI packet may be transmitted bythe base station to the UA for each traffic packet/sub-frametransmission.

In some network implementations, relay nodes (RNs) may be includedamongst the various network components to efficiently extend a UA'sbattery life and increase UA throughput. For example, in some networks,base stations and RNs may work together to transmit the same signal to aUA at the same time. In such a system, the signals transmitted by thebase station and RN may combine (i.e., superpose) in the air to providea stronger signal and thus increase the chance of transmission success.In other networks, base stations and RNs transmit different signals tothe UA, which, for example, include different data that is to becommunicated to the UA. By transmitting different portions of the datathrough different base stations and/or RNs, the throughput to the UA maybe increased. The use of a combination of base stations and RNs dependson many factors including channel conditions at the UA, availableresources, Quality of Service (QoS) requirements, etc. As such, in somenetwork implementations, in a given cell or combination of cells only asubset of available UAs may be serviced with combinations of basestations and RNs.

FIG. 1 is an illustration of a wireless communications network thatincorporates base stations and RNs for transmitting data to a UA.Several RNs 100 are positioned around the edges of cells 102 and 104.The network includes several base stations 12 for coordinating networkcommunications, which may include eNBs. The combination of RNs 100 andbase stations 12 communicate with UAs 10. In FIG. 1, UA 10 a is servedby a lone RN 100 a. Because RNs 100 are distributed about the edge ofcells 102 and 104, UAs 10 can access the network at a higher data rateor lower power consumption by communicating directly with RNs 100 ratherthan base stations 12.

In a network that includes RNs in combination with base stations, therecan be significant difference between the base station's transmissionpower (e.g., 46 dBm) and an RN's transmission power (e.g. 30 dBm). Thedifference in transmission power can lead to different coverage areasfor both the RNs and base stations. In any network, however, the UA hasonly a single transmission power for signals transmitted to the RNand/or the base station and the received power for such a signal isdependent on the propagation path between the UA and the RN or the basestation. As such, there may be times when the UA receives a strongerdownlink (DL) transmission from the base station than from an RN whilethe RN receives a stronger uplink (UL) UA transmission than the basestation. This situation results in an uplink/downlink (UL/DL) imbalancesituation. In UL/DL imbalance, on the UL, the best serving node (e.g.,base station or RN) may be the one that has the smallest coupling loss(e.g., path loss plus the transmit and receive antenna gains) with theUA while on the DL, the best serving node may be the one that providesthe strongest DL received power at the UA (i.e., includes the transmitpower of the node besides the coupling loss).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is an illustration of a wireless communications network thatincorporates base stations and relay nodes (RNs) for transmitting datato a user agent (UA);

FIG. 2 is a schematic diagram illustrating an exemplary multi-channelcommunication system including a UA and an access device;

FIG. 3 illustrates a network simulation that includes two RNs placed at¾ radius away from a base station at 70 and 110 degrees;

FIG. 4 is an illustration of simulation results for the networkconfiguration illustrated in FIG. 3;

FIG. 5 is an illustration of the uplink (UL) coupling loss comparisonsamong the four assignment schemes when applied to the simulation data ofFIG. 4;

FIG. 6 is an illustration of comparisons of the UA downlink (DL) receivepower among the four schemes when applied to the simulation data of FIG.4;

FIG. 7 is a flow chart illustrating an example method for implementingthe UA association algorithm of the present system;

FIG. 8 illustrates a flow chart showing a general method for Modulationand Coding Scheme (MCS) selection and for modifying a transmission powerlevel of a UA;

FIGS. 9-12 are illustrations of alternative flowcharts for implementingthe UA link and power level adaptation algorithms of the presentdisclosure;

FIG. 13 illustrates the various network entities that participate ininner loop and outer loop link adaptation algorithms of FIGS. 8-11;

FIG. 14 is a diagram of a wireless communications system including a UAoperable for some of the various embodiments of the disclosure;

FIG. 15 is a block diagram of a UA operable for some of the variousembodiments of the disclosure;

FIG. 16 is a diagram of a software environment that may be implementedon a UA operable for some of the various embodiments of the disclosure;and

FIG. 17 is an illustrative general purpose computer system suitable forsome of the various embodiments of the disclosure.

DETAILED DESCRIPTION

The present invention relates generally to data transmission incommunication systems and more specifically to methods and systems forassociation and uplink adaptation and power control in a relay network.

Some embodiments include a method for allocating resources of a wirelesscommunication system. The wireless communication system includes a basestation and a plurality of relay nodes (RNs). The method includesdetecting power levels of downlink (DL) communication channels betweenthe base station and a user agent (UA) and between each of the pluralityof RNs and the UA, and detecting coupling losses of uplink (UL)communication channels between the base station and the UA and betweeneach of the plurality of RNs and the UA. When the power level of the DLcommunication channel between the base station and the UA is greaterthan the power levels of the DL communication channels between each ofthe plurality of RNs and the UA, and the coupling losses of the ULcommunication channel between at least one of the RNs and the UA areless than the coupling losses of the UL communication channel betweenthe base station and the UA, the method includes allocating a DLcommunication channel resource on the base station to the UA, andallocating a UL communication channel resource on the at least one ofthe plurality of RNs to the UA.

Other embodiments include a method for allocating resources of awireless communication system. The wireless communication systemincluding a base station and a plurality of relay nodes (RNs). Themethod includes receiving sounding reference signals (SRSs) from atleast one of a UA and the plurality of RNs. The SRSs describe powerlevels of uplink (UL) communication channels between the UA and the basestation and between the UA and each of the plurality of RNs. When apower level of a UL communication channel between the UA and at leastone of the plurality of RNs is greater than the power level of the ULcommunication channel between the UA and the base station, identifyingone of the RNs having the UL communication channel with the greatestpower level out of the plurality of RNs, the method includes determininga receiving power of the UA from the base station and a receiving powerof the UA from one of the plurality of RNs. When the receiving power ofthe UA from the base station is greater than the receiving power of theUA from one of the plurality of RNs, the method includes allocating ULcommunication channel resources on both the base station and the one ofthe plurality of RNs to the UA, and allocating a downlink (DL)communication channel resource on the base station to the UA.

Other embodiments include a base station for allocating resources of awireless communication system. The wireless communication systemincludes the base station and a plurality of relay nodes (RNs). The basestation includes a processor. The processor is configured to detectpower levels of downlink (DL) communication channels between the basestation and a user agent (UA) and between each of the plurality of RNsand the UA, and detect coupling losses of uplink (UL) communicationchannels between the base station and the UA and between each of theplurality of RNs and the UA. Instead of detecting coupling losses ofuplink (UL) communication channels between the base station and the UAand between each of the plurality of RNs and the UA, another embodimentis to detect the coupling loss difference between the uplinkcommunications channels between the base station and the UA and betweeneach of the plurality of RNs and the UA. When the power level of the DLcommunication channel between the base station and the UA is greaterthan the power levels of the DL communication channels between each ofthe plurality of RNs and the UA, and the coupling losses of the ULcommunication channel between at least one of the RNs and the UA areless than the coupling losses of the UL communication channel betweenthe base station and the UA, the processor is configured to allocate aDL communication channel resource on the base station to the UA, andallocate a UL communication channel resource on the at least one of theplurality of RNs to the UA.

Other embodiments include a base station for allocating resources of awireless communication system. The wireless communication systemincludes the base station and a plurality of relay nodes (RNs). The basestation includes a processor. The processor is configured to receivesounding reference signals (SRSs) from at least one of a UA and theplurality of RNs. The SRSs describe power levels of uplink (UL)communication channels between the UA and the base station and betweenthe UA and each of the plurality of RNs. When a power level of a ULcommunication channel between the UA and at least one of the pluralityof RNs is greater than the power level of the UL communication channelbetween the UA and the base station, identify one of the RNs having theUL communication channel with the greatest power level out of theplurality of RNs, the processor is configured to determine a receivingpower of the UA from the base station and a receiving power of the UAfrom one of the plurality of RNs. When the receiving power of the UAfrom the base station is greater than the receiving power of the UA fromone of the plurality of RNs, the processor is configured to allocate ULcommunication channel resources on both the base station and the one ofthe plurality of RNs to the UA, and allocate a downlink (DL)communication channel resource on the base station to the UA.

Other embodiments include a method for determining a Modulation andCoding Scheme (MCS) for a wireless communication system. The wirelesscommunication system includes a base station and a relay node (RN). Atleast one of the base station and the RN is configured to communicatewith a user agent (UA) using at least one of an uplink (UL) and downlink(DL) communication channel. The method includes defining an MCS using atleast one of a signal quality value of the communication channel betweenthe UA and the base station, a coupling loss between the UA and the basestation, and a coupling loss between the UA and the RN, and detecting anerror rate of a communication channel between the UA and at least one ofthe base station and the RN. When the error rate is below a threshold,the method includes at least one of increasing the MCS, and reducing atransmission power of the UA. When the error rate is above a threshold,the method includes at least one of decreasing the MCS, and increasing atransmission power of the UA.

Other embodiments include a method for determining a Modulation andCoding Scheme (MCS) for a wireless communication system. The wirelesscommunication system includes a base station and a relay node (RN). Atleast one of the base station and the RN is configured to communicatewith a user agent (UA) using at least one of an uplink (UL) and downlink(DL) communication channel. The method includes detecting an error rateof a communication channel between the UA and at least one of the basestation and the RN. When the error rate is below a threshold, the methodincludes at least one of increasing the MCS, and reducing a transmissionpower of the UA. When the error rate is above a threshold, the methodincludes at least one of decreasing the MCS, and increasing atransmission power of the UA.

Other embodiments include a base station for determining a Modulationand Coding Scheme (MCS) for a wireless communication system. Thewireless communication system includes the base station and a relay node(RN). At least one of the base station and the RN is configured tocommunicate with a user agent (UA) using at least one of an uplink (UL)and downlink (DL) communication channel. The base station includes aprocessor. The processor is configured to define an MCS using at leastone of a signal quality value of the communication channel between theUA and the base station, a coupling loss between the UA and the basestation, and a coupling loss between the UA and the RN, and detect anerror rate of a communication channel between the UA and at least one ofthe base station and the RN. When the error rate is below a threshold,the processor is configured to at least one of increase the MCS, andreduce a transmission power of the UA. When the error rate is above athreshold, the processor is configured to at least one of decrease theMCS, and increase a transmission power of the UA.

Other embodiments include a base station for determining a Modulationand Coding Scheme (MCS) for a wireless communication system. Thewireless communication system including the base station and a relaynode (RN). At least one of the base station and the RN is configured tocommunicate with a user agent (UA) using at least one of an uplink (UL)and downlink (DL) communication channel. The base station includes aprocessor. The processor is configured to detect an error rate of acommunication channel between the UA and at least one of the basestation and the RN. When the error rate is below a threshold, theprocessor is configured to at least one of increase the MCS, and reducea transmission power of the UA. When the error rate is above athreshold, the processor is configured to at least one of decrease theMCS, and increase a transmission power of the UA.

Other embodiments include a wireless communication system, comprising auser agent (UA) for communicating with a base station and a relay node(RN). The UA is configured to receive an instruction from the basestation. The instruction may specify a Modulation and Coding Scheme(MCS) or instruct the UA to modify a power level of the UA. The systemincludes a base station configured to define an MCS and to detect anerror rate of a communication channel between the UA and at least one ofthe base station and the RN. When the error rate is below a threshold,the base station is configured to transmit an instruction to the UAincluding at least one of an increased MCS and a reduced transmissionpower specification. When the error rate is above a threshold, the basestation is configured to transmit an instruction to the UA including atleast one of a decreased MCS and an increased transmission powerspecification.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described. The followingdescription and the annexed drawings set forth in detail certainillustrative aspects of the invention. However, these aspects areindicative of but a few of the various ways in which the principles ofthe invention can be employed. Other aspects and novel features of theinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the drawings.

The various aspects of the subject invention are now described withreference to the annexed drawings, wherein like numerals refer to likeor corresponding elements throughout. It should be understood, however,that the drawings and detailed description relating thereto are notintended to limit the claimed subject matter to the particular formdisclosed. Rather, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theclaimed subject matter.

As used herein, the terms “component,” “system” and the like areintended to refer to a computer-related entity, either hardware, acombination of hardware and software, software, or software inexecution. For example, a component may be, but is not limited to being,a process running on a processor, a processor, an object, an executable,a thread of execution, a program, and/or a computer. By way ofillustration, both an application running on a computer and the computercan be a component. One or more components may reside within a processand/or thread of execution and a component may be localized on onecomputer and/or distributed between two or more computers.

The word “exemplary” is used herein to mean serving as an example,instance, or illustration. Any aspect or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs.

Furthermore, the disclosed subject matter may be implemented as asystem, method, apparatus, or article of manufacture using standardprogramming and/or engineering techniques to produce software, firmware,hardware, or any combination thereof to control a computer or processorbased device to implement aspects detailed herein. The term “article ofmanufacture” (or alternatively, “computer program product”) as usedherein is intended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. For example, computerreadable media can include but are not limited to magnetic storagedevices (e.g., hard disk, floppy disk, magnetic strips . . . ), opticaldisks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ),smart cards, and flash memory devices (e.g., card, stick). Additionallyit should be appreciated that a carrier wave can be employed to carrycomputer-readable electronic data such as those used in transmitting andreceiving electronic mail or in accessing a network such as the Internetor a local area network (LAN). Of course, those skilled in the art willrecognize many modifications may be made to this configuration withoutdeparting from the scope or spirit of the claimed subject matter.

Referring now to the drawings wherein like reference numerals correspondto similar elements throughout the several views, FIG. 2 is a schematicdiagram illustrating an exemplary multi-channel communication system 30including a UA 10 and an access device 12. Although not shown, thecommunication system 30 may include one or more RNs in communicationwith UA 10. UA 10 includes, among other components, a processor 14 thatruns one or more software programs wherein at least one of the programscommunicates with access device 12 to receive data from, and to providedata to, access device 12. When data is transmitted from UA 10 to device12, the data is referred to as uplink data and when data is transmittedfrom access device 12 to UA 10, the data is referred to as downlinkdata. Access device 12, in one implementation, may include a basestation such as an E-UTRAN node B (eNB), a relay node (RN) or othernetwork component for communicating with UA 10.

To facilitate communications, a plurality of different communicationchannels are established between access device 12 and UA 10. For thepurposes of the present disclosure, referring to FIG. 2, the importantchannels between access device 12 and UA 10 may include a PhysicalDownlink Control CHannel (PDCCH) 70, a Physical Downlink Shared CHannel(PDSCH) 72 and a Physical Uplink Shared CHannel (PUSCH) 74. As the labelimplies, the PDCCH is a channel that allows access device 12 to controlUA 10 during downlink data communications. To this end, the PDCCH can beused to transmit scheduling or control data packets referred to asdownlink control information (DCI) packets to the UA 10 to indicatescheduling to be used by UA 10 to receive downlink communication trafficpackets or transmit uplink communication traffic packets or specificinstructions to the UA (e.g. power control commands, an order to performa random access procedure, a semi-persistent scheduling activation ordeactivation). A separate DCI packet may be transmitted by access device12 to UA 10 for each traffic packet/sub-frame transmission. ExemplaryDCI packets are indicated by communication 71 on PDCCH 70 in FIG. 1.Exemplary traffic data packets or sub-frames on pdsch 72 are labeled 73.The PUSCH 74 is used by UA 10 to transmit data sub-frames or packets toaccess device 12. Exemplary traffic packets on PUSCH 74 are labeled 77.

In a wireless communications network, RNs may be included amongst thevarious network components to efficiently extend a UA's battery life andincrease UA throughput. In such a network, however, there can be adifference between the base station's transmission power (e.g., 46 dBm)and an RN's transmission power (e.g. 30 dBm) that leads to differentcoverage areas and sizes for both the RNs and base stations. In anynetwork, however, the UA has only a single uplink (UL) transmissionpower for signals that may be received by the RN and/or the basestations and the received power for such a signal is dependent on thepropagation path loss between the UA and the RN or base station. Assuch, there may be times when the UA receives a stronger DL transmissionfrom the base station than from an RN while the RN receives a strongerUL UA transmission than the base station. This situation results in anuplink/downlink (UL/DL) imbalance. In UL/DL imbalance, on the UL, thebest serving node (e.g., base station or RN) may be the one that has thesmallest coupling loss (e.g., path loss plus antenna gains) with the UA,while on the DL, the best serving node may be the one that provides thestrongest DL received power at the UA (i.e., includes the transmit powerof the node besides the coupling loss).

It is possible to simulate the impact of UL/DL imbalance. FIG. 3illustrates a network simulation that includes two RNs 120 and 122placed at ¾ radius away from a base station 124 at 70 and 110 degrees.In the simulation 700 UAs were placed uniformly in the cell sectorcontaining RNs. Only path loss and shadowing are considered (fast fadingis not considered). For the simulation, Table 1 shows the detailedsimulation parameters. Using the simulation, it is possible todemonstrate the UL/DL imbalance that may result from a networkconfigured as illustrated in FIG. 3.

TABLE 1 Parameter Assumption/Values Cellular layout 19 cells 57 sectorsRelay layout 2 RNs per macro eNB cell Inter-site distance (ISD) 1732 mPath loss for eNB <-> UA L = 128.1 + 37.6 log10(R), R in kilometers Pathloss for RN <-> UA L = Prob(R) PLLOS(R) + [1 − Prob(R)]PLNLOS(R), R inkm PLLOS(R) = 103.8 + 20.9log10(R) PLNLOS(R) = 145.4 + 37.5log10(R)Prob(R) = 0.5 − min(0.5, 3exp (−0.3/R)) + min(0.5, 3exp(−R/0.095))Shadowing standard deviation 10 dB (RN to UA); 8 dB (eNB to UA)Shadowing correlation 0.5 between sites (including eNB and RN); 1between cells per site Antenna pattern (horizontal) eNB: beamwidth 70degrees, Am = 20 dB. RN: omni-directional${A(\theta)} = {- {\min \left\lbrack {{12\left( \frac{\theta}{\theta_{3d\; B}} \right)^{2}},A_{m}} \right\rbrack}}$Minimum distance between 35 m between UA and eNB UA and eNB Tx power 46dBm for eNB, 30 dBm for RN BS antenna gain 14 dBi Relay antenna gain 5dBi.

FIG. 4 illustrates simulation results for the network configurationillustrated in FIG. 3 with the x-axis representing the UA's horizontaldistance in meters from base station 124 and the y-axis representing theUA's vertical distance in meters from base station 124. Each pointillustrates a UA in either a first, second or third category. As shownin FIG. 4, nearly 69.6% of the UAs are in a first category illustratedby dots on FIG. 4. The first category represent UAs where the strongestDL receive power and the smallest UL coupling loss are both with basestation 124 (i.e., it is preferable that both UL and DL communicationschannels be served by base station 124). As shown in FIG. 4, 12.7% ofthe UAs are in the second category (shown by Xs in FIG. 4) indicatingthe UA's best UL coupling loss and DL receive power would be with eitherRN 120 or 122 (i.e., it is preferable that both UL and DL communicationchannels be served by either RN 120 or 122, but not by base station124). Finally, 17.7% of the UAs are in the third category (shown by Osin FIG. 4) indicating that the UAs are in the UL/DL imbalance region. Assuch, the UAs in the third category have the strongest DL receive powerfrom base station 124 while the smallest UL coupling loss is with eitherRN 120 or 122.

Using the cumulative distributions of the UL coupling loss and DLreceiving power for each of the UAs as illustrated in the results ofFIG. 4, it is possible to define four independent schemes that may beused to associate each UA with base station 124, RNs 120 or 122, or acombination thereof.

The first assignment scheme is base station only. For example, all ofthe 700 UAs defined in the simulation may be configured to operate as ifno RN is available.

The second assignment scheme is a first relay transmission scheme, inwhich all of the 700 UAs receive from and send to a single node (e.g.,base station or RN) to which the UAs have the lowest coupling loss.

The third assignment scheme is a second relay transmission scheme, inwhich all of the 700 UAs receive from and send to the node (e.g., basestation or RN) from which the strongest DL receiving power is received.

The fourth assignment scheme is an imbalanced scheme, in which all ofthe 700 UAs receive from the node (e.g., base station or RN) thatprovides the greatest DL power and the UA transmits to the node (e.g.,base station or RN) to which the UA has the lowest coupling loss.

FIG. 5 is an illustration of the UL coupling loss comparisons among thefour assignment schemes when applied to the simulation data of FIG. 4.FIG. 5 shows Cumulative Distribution Function (CDF) of the UL couplingloss in dB (shown on the x-axis) for each of the four assignmentschemes. Both the first relay transmission scheme and the imbalancedscheme achieve the smallest coupling loss. Compared to the basestation-only scheme, the second relay transmission scheme may reduce, onaverage, 4.1 dB UA coupling loss while the first relay transmissionscheme and the imbalanced scheme may both reduce, on average, 5.4 dB UAcoupling loss. In some cases, smaller UA coupling losses may lead to UAstransmitting with lower power that may cause less UL interference andsave UA battery power.

FIG. 6 is an illustration of comparisons of the UA DL receive poweramong the four schemes when applied to the simulation data of FIG. 4.FIG. 6 shows the Cumulative Distribution Function of the UA DL receivingpower (shown on the x-axis) for each of the four assignment schemes. Thefirst relay transmission scheme may achieve, on average, 0.3 dB less DLreceive power than with the base station-only scheme because some of theUAs operate in the imbalanced region. The imbalanced UAs select the RNover the base station as the DL receiving node resulting in a smallerreceive power on the DL. On the other hand, the second relaytransmission scheme and the imbalance transmission scheme show a 1.79 dBhigher average DL receiving power than with the base station-onlytransmission scheme. The second relay transmission scheme and theimbalanced transmission scheme, therefore, may maximize the average DLreceiving power by allowing the UAs in the imbalanced region to receiveDL transmission directly from the base station. Stronger DL receivingpower means better overall throughput and better QoS.

Generally, the first relay transmission scheme minimizes UL couplingloss but results in a reduced DL receive power while the second relaytransmission scheme maximizes the UA DL receive power but results inhigher UL coupling loss. The imbalanced scheme, on the other hand, maysimultaneously minimize UL coupling loss and maximize the UA DL receivepower.

In a network that incorporates one or more RNs, the RNs may beconfigured to assist a base station with DL and/or UL transmissions toor from a UA. Because a UA may be associated with one or more basestation and/or RN, UA association types can be defined to classify theconnection between the UA and the base station and/or RN.

In a first association type, a UA is associated with only the basestation. In the first association type, no available RNs may participatewith any transmissions to or from that UA. As a result, the RN does notneed to decode PDCCH channels with DCI format 0 (UL scheduling grant)and with DCI formats 1 and 2 (DL scheduling grants) for that UA.

In a second association type, a UA is associated with the base stationand an RN for both UL and DL communications. In this case, the RN mayparticipate with both UL and DL transmissions to or from that UA. Assuch, the RN may need to decode all PDCCH channels with DCI formats 0,1, and 2 for UL and DL communications with that UA.

In a third association type, a UA is associated with an RN only on ULtransmissions, but with a base station for both UL and DL transmissions.In that case, the RN may only participate with a UA's UL transmissions.As such, the RN may only need to decode the PDCCH channel with DCIformat 0 for UL communications with the UA.

In a fourth association type, a UA is associated with an RN only for DLtransmissions, but with a base station for both UL and DL transmissions.In this case, the RN may only participate with the UA's DLtransmissions. As such, the RN may only need to decode the PDCCHchannels with DCI formats 1 and 2 for that UA.

In the present system, therefore, a base station may be configured todetermine whether a UA is operating 1) with the strongest DL receivepower and the smallest UL coupling loss being both with the basestation, 2) with the UA's best UL coupling loss and DL receive powerbeing with an RN, or 3) where the UAs are in the UL/DL imbalancedregion. Based upon the determination, the base station may allocate oneof the association types to the UA causing the UA to be assigned UL andDL communication channel resources on a base station and an RN, or acombination of RNs. The various association types that may be allocatedto a UA are summarized in Table 2.

TABLE 2 Association Type UL with DL with 1 Base Station Base Station 2Base Station + RN Base Station + RN 3 Base Station + RN Base Station 4Base Station Base Station + RN

If the base station determines that the UA should be associated with anRN, the base station may use any available measurement data to determinethe RN to which the UA should be associated. For example, in LTE orLTE-Advanced, the UA may transmit UL Sounding Reference Signals (SRSs)or other UL control channels (e.g., PUCCH) for channel qualitymeasurements and uplink timing estimation. For example, for all UAsassociated with a particular base station, the base station may forwardthe UA's SRS or control channel configurations (potentially includingmonitoring parameters) to all the RNs accessible to the base station forassociation purposes. As such, the RNs may monitor the SRS transmissionsfrom all UAs, forward the measurements to the base station and then thebase station may determine the RN to which the UA may be near and withwhich the UA should be associated. The base station can also use thesame method, i.e. RNs monitoring SRS transmissions from the UAs andforwarding the measurements to the base station, to decide whether a UAshould be associated with only the base station or with one of the RNs.

In one implementation of the present system, UA transmission power perresource element (RE) (PUA) minus the UA's coupling loss with the basestation (CeNB) is equal to the power density of the SRS received by thebase station (ULeNB_P). Also, PUA minus the UA's coupling loss with RNi(Crelay_i) is equal to the power density of the SRS received by RNi(ULrelay_P_i), ULrelay_P_i−ULeNB_P=CeNB−Crelay_i. Given the foregoing,the following examples describe various algorithms for analyzing thecoupling loss and DL received power of a UA for allocating one of thefour association types as described above. In the following examples,the notations as illustrated in Table 3 are used.

TABLE 3 Symbols Stand for UL_eNB_P The power density of the SRS receivedby the base station UL_relay_P_i The power density of the SRS receivedby RN i UL_eNB_Q The channel quality estimated from the SRS received bythe base station UL_relay_Q _i The channel quality estimated from theSRS received by RN i P_eNB base station transmission power P_relay_i RNi transmission power. C_eNB UA's coupling loss with the base stationC_relay_i UA's coupling loss with the RN i P_UA UA transmission powerper RE P_eNB-C_eNB UA DL receiving power from base station P_relay_i- UADL receiving power from RN i C_relay_i

In the present example, if the difference between the power of the SRSreceived by the base station and each RN is greater than or equal to apre-defined margin (ULeNB_P−ULrelay_P_i>margin0), for all i, the UA ULcommunication channel may be associated with the base station only. Inthis example, margin0 defines a micro-diversity range to ensure that theUA's UL association with the base station only may lead to asufficiently small coupling loss on the UL channel.

Then, if the base station transmission power received by the UA isgreater than RN transmission power received by the UA by a predefinedmargin (PeNB−CeNB>Prelay_i−Crelay_i+margin1 or, equivalently,PeNB−Prelay_i>ULrelay_P_i−ULeNB_P+margin1), for all i, the UA DL is alsoassociated with the base station only. This corresponds to the firstassociation type described above.

If, however, the base station transmission power received by the UA isnot greater than RN transmission power received by the UA by apredefined margin (in other words, there exists at least one integer i,such that PeNB−CeNB<=Prelay_i−Crelay_i+margin1 or, equivalently,PeNB−Prelay_i<=ULrelay_P_i−ULeNB_P+margin1), the system first definesthe set of RNs as Ω such that every RN belonging to Ω meets thiscriteria. Then the system selects the RN within Ω with the greatesttransmission power received by the UA. (In other words, the systemselects RNj in the set Ω such that Prelay_j−Crelay_j is the largest) TheUA may then be associated with both the base station and RNj for DLcommunications. This corresponds to the fourth association typedescribed above.

Alternatively, if there exists at least one integer i such that thedifference between the power of the SRS received by the base station andeach RNi is less than a pre−defined margin (e.g.,ULeNB_P−ULrelay_P_i<margin0), define the set of RNs as Ω such that everyRN belonging to Ω meets this criteria. Then the system selects the RNwithin Ω with the highest power SRS received by the RN, (in other words,the system selects RNj in set Ω such that ULrelay_P_j is the largest).

Then, if the base station's transmission power minus the base station'scoupling loss is greater than RNj's transmission power minus the RNj'scoupling loss plus a margin (e.g., PeNB−CeNB>Prelay_j−Crelay_j+margin1or equivalently PeNB−Prelay_j>ULrelay_P_j−ULeNB_P+margin1), the UA maybe associated with the base station for DL communications and associatedwith both the base station and RNj for UL communications. Thiscorresponds to the third association type as described above. In thiscase, margin1 defines a macro-diversity range to ensure that the UA's DLassociation with only the base station may lead to a sufficiently strongDL receiving power from the base station.

If, however, the base station's transmission power minus the basestation's coupling loss is not greater than RNj's transmission powerminus the RN's coupling loss plus a margin (e.g.,PeNB−CeNB<=Prelay_j−Crelay_j+margin1 or equivalentlyPe_NB−Prelay_j<=ULrelay_P_j−ULeNB_P+margin1), the UA may be associatedwith the base station and RNj for both UL and DL communications. Thiscorresponds with the second association type as described above.

FIG. 7 is a flow chart illustrating an example method for implementingthe UA association algorithm of the present system. In step 150, foreach base station and every UA that has selected the base station as theUA's serving base station, the system starts a procedure to decide theUA's association type. To determine the association type, in step 152,the system evaluates whether the power of SRS received by the basestation is greater than the power of SRS received by any of the RNs fora particular UA. For example, in FIG. 7, the system evaluates whetherULeNB_P>ULrelay_P_i+margin0 for all i. If not, and the power of the SRSreceived by one of the available relay nodes is greater than the powerreceived by the base station minus margin0, in step 154 the systemdetermines which relay node receives the signal having the greatestpower. For example, for i in the set of RNs Ω, the system selects the RNin Ω that has the largest ULrelay_P and denotes it as RNj. In step 158,the system then allocates association types based upon the downlinkreceiving power, which is determined by the difference of thetransmission powers of the base station and selected RN, and thedifference in the SRS powers received by the base station and selectedRN. For example, if PeNB−Prelay_j>ULrelay_P_j−ULeNB_P+margin1, thesystem associates the UA with association type 3 in step 166. If not,the system associates the UA with association type 2 in step 168.

In step 156, if the power of SRS received by the base station is greaterthan the power of SRS received by any of the relay nodes, the systemevaluates the downlink receiving power of the base station and the relaynode by determining whether the difference of the transmission powers ofthe base station and RN is greater than the difference in the SRS powersreceived by the base station and RN for all the available RNs. Forexample, the system evaluates PeNB−Prelay_i>ULrelay_P_i−ULeNB_P+margin1for all RNs i If the difference of the transmission powers of the basestation and RN is greater than the difference in the SRS powers receivedby the base station and RN for all available RNs, the system allocatesthe UA the first association type in step 164. If not, the systemselects the RN that has the largest transmission power(Prelay_j)+received SRS power (ULrelay_P_j) and associates the UA withthe selected RN and the base station for DL communications and with thebase station only for UL communications. In step 162, the systemallocates the UA the fourth association type.

In the UA association algorithm illustrated in FIG. 7, the UAs in thefirst category of FIG. 4 (i.e., those UA's having the strongest DLreceive power and the smallest UL coupling loss both with the basestation) may most likely be allocated the first association type, whilethe UAs in the second category (i.e., the UA's best UL coupling loss andDL receive power are with an RN) may most likely be allocated the secondassociation type. The UAs in the imbalance region (the third category)may most likely be allocated the third association type. The fourthassociation type may be allocated when the RN transmission power islarger than that of the base station with a certain margin (e.g.,Prelay>Pbase_station+margin0−margin1). In the imbalanced region, thebase station may have better DL coverage while RNs have better ULcoverage. As such, UAs in the imbalanced region may not need RNs toparticipate in DL transmission but may need RNs to participate in ULtransmission. The addition of the third association type may help reduceDL interference to other sectors and also reduce RN PDCCH blind decodingcomplexity as well as backhaul traffic load (e.g., the base station doesnot need to transmit these UAs' DL control and data to an RN). Thebigger the imbalanced region, the more performance gain the presentassociation algorithm may achieve. Note also that the presentassociation algorithm may reduce both the DL interference and backhaultraffic load in a particular implementation. For example, for the thirdassociation type, the RN may only assist the UL transmission from theUA. This may reduce the DL interference caused by the RN as well asreducing the traffic over the wireless backhaul link (e.g., the basestation does not need to transmit the UA's DL control and data to theRN).

In a network that incorporates one or more RNs, as discussed above, theRNs may be configured to participate in a UA's UL and DL transmissions.In the case of UL transmissions, a UA may send the first transmissiondirectly to both the base station and an RN. If the first transmissionto the base station fails, starting for the first retransmission, thebase station may be configured to receive UL data from both the UA andthe RN. Because synchronous non-adaptive Hybrid Automatic Repeat reQuest(HARQ) may be used in UL transmissions, the same Modulation and CodingScheme (MCS) may be used in the first transmission as well as allretransmissions. Due to the nature of the above-described RN-assisted ULtransmissions, however, it is difficult to determine, based upon thechannel conditions between the UA and eNB, which MCS to select for ULtransmissions. In accordance with the present system, there are severalpossible ways to select the MCS.

First, the MCS may be selected based upon the UA to base station channelconditions. In that case, however, the MCS may be too conservative ifthe potential assistance that could be provided by an RN is notconsidered. Second, the MCS may be selected based upon the UA to RNchannel conditions. This example, however, may not be reliable becausethe algorithm relies upon the UA to RN channel that is not a direct linkto the base station. Third, the MCS may be selected based upon the RN tobase station channel. Again, this may not be a reliable algorithm forselecting the MCS because the RN to base station link is only activewhen the UA to RN communication link is functional.

Generally, the channel quality on all three links (UA to base station,UA to RN, and RN to base station) may affect the MCS selection.Therefore, to maximize the benefits of the RN, the link adaptation maybe based on a virtually combined channel that incorporates featuresand/or characteristics of all three links. Because it may be difficultfor the base station to estimate the instantaneous combined channelconditions, an outer loop link adaptation and Close Loop Power Control(CLPC) may be used to adjust the MCS level and UA transmission powerlevel based on a long term criteria such as a desired UA Frame ErasureRate (FER) and/or HARQ target termination, on top of an Open Loop PowerControl (OLPC) and inner loop link adaptation, which is based oninstantaneous channel quality information and estimations.

For the OLPC, the power level may be set using a first option based uponUA to base station path loss, which may be estimated in accordance withconventional procedures. In some cases, however, because the RN may nottransmit Cell-specific Reference Signals (CRSs), the path loss of the UAto RN channel may not be estimated using conventional methods. In thatcase, the power level may be set using a second option based on the UAto base station path loss plus an offset. The offset may be equal toCrelay−CeNB, which is the coupling loss difference between the UA tobase station link and the UA to RN, or can be a function ofCrelay−CeNB). The offset can be estimated using relative UL soundingsignal strength differences between the UA to RN link and the UA to basestation link. The base station may then signal the coupling lossdifference to the UA and the UA can adjust the power offset accordingly.In some implementations, the base station may signal the appropriateP_(O) _(_) _(UA) _(_) _(PUSCH) value that already includes the couplingloss difference to the UA.

In the above examples, the second option may lead to a lower powersetting for the UA than the first option. Control signals such asACK/NACK are often more delay stringent and are preferred to be directlyreceived by the base station. As such, it may be preferable that powersettings for the control signal be based on UA to base station pathloss. Different power settings for UL control signals and data signalsare feasible in Rel-8 when they are not transmitted simultaneously. Insome cases, for example, for Rel-8 UAs, the OLPC may always be based onthe first option and for Rel-10 UAs the OLPC may be based on the secondoption as described above.

FIG. 8 illustrates a flow chart showing a general method for MCSselection and for modifying a transmission power level of a UA inaccordance with the present disclosure. The first step 180 is for systeminitialization. In step 182, an MCS is selected based upon the UL signalquality between the base station (e.g., an eNB) and the UA and thecoupling loss between the UA and base station and the UA and RN. Forexample, the system may select the MCS based upon the UA to base stationsignal quality, plus the difference between the UA to base stationcoupling loss and the UA to RN coupling loss, plus an offset.Alternatively, the MCS may be selected based upon the UA to RN UL signalquality plus an offset.

In step 184, after selecting an MCS, various system performance metricsare captured and analyzed to assist in determining whether the selectedMCS is appropriate. For example, after completion of each ULtransmission, the system may detect a failure due to a maximum number ofHARQ retransmissions being reached or a success before the maximumnumber of HARQ retransmissions is not reached. In step 184, UAperformance metrics such as HARQ statistics and Frame Erasure Rate (FER)are updated.

In step 186, the performance metrics are analyzed to determine whetherthe currently selected MCS and power levels are appropriate and whetherany changes are necessary. For example, in step 186, the system maydetermine whether the current UA performance is too good (e.g., UA FERis too low and HARQ termination is too early). If so, the offset valuemay be changed to increase the MCS level, or the UA transmission powermay be reduced. Alternatively, if the current performance of the UA istoo bad (e.g., UA FER is too high or HARQ termination number is toohigh), the offset may be changed to reduce the MCS level or increase theUA transmission power. Finally, if the current UA performance isacceptable, the system may take no action and continue operation asnormal. After modifying the MCS and UA power levels as necessary in step186, the process repeats for future communications with the UA.

FIGS. 9-11 illustrate specific algorithms for implementing the generalalgorithm illustrated in FIG. 8. In a first specific implementation ofthe present system, as illustrated in FIG. 9, at the start of each newtransmission, an MCS that targets a 10% BLock Error Rate (BLER) selectedon the first termination in step 200. In these examples, when doing MCSselection and resource allocation, the base station may consider UApower headroom so that the maximum power of the UA may not be exceededand also to allow the base station to select an MCS that results in aparticular transmission power level at the UA. Power headroom may becomputed by the UA based on the UA's current transmit power on the PUSCHand its maximum transmission power and the UA will send the powerheadroom report to the base station.

In step 200, the MCS may be selected using several options. First, if UAOLPC is based on UA to base station path loss, the base station maydetermine the MCS based on the channel quality estimation of the UA tobase station link plus an offset. The channel quality estimation of theUA to base station link can be done, for example, using any existingRel-8 mechanisms. In one example, the offset may be ΔSRS+the couplingloss difference between UA to base station (i.e., ΔSRS+CeNB−Crelay). Inthis example, ΔSRS may be used to compensate the combined channel gain.The offset may initially be set to 0 and dynamically adjusted based onthe UA QoS and performance requirements, e.g., HARQ terminationstatistics and FER.

Alternatively, if UA OLPC is based on UA to RN path loss, the basestation may determine the MCS based on channel quality estimation of theUA to RN link plus an offset ΔSRS. ΔSRS may be defined and adapted thesame way as described above. In this case, however, the RN may need toperiodically send UA to RN channel related information (for example,ULSRS and PUSCH Signal to Noise and Interference Ratio (SNIR)) to thebase station through the wireless backhaul link so that the base stationhas knowledge of the UA to RN channel condition. To save bandwidth onbackhaul, the channel information report can be sent in a delta formatand is only needed when such delta reaches a certain threshold.

In step 202, after each UL transmission terminates (success or failure),the base station updates UA QoS related measurements, for example, theaverage number of HARQ transmissions and average Frame Erasure Rate(FER). In some implementations, the average is a window-based movingaverage. For a delay-critical application like Voice over InternetProtocol (VoIP), the system may use the ath percentile of HARQtransmission numbers, for example a=95, instead of average HARQtransmission numbers to do adaptation. Performing adaptation using thismethod, for example, may better control the 95th percentile delay, whichmay be defined by various network standards. Note that, FER is ameasurement of the percentage of Transport Blocks (TB) that containerrors and could not be processed at the base station side after themaximum number of HARQ transmissions is reached.

In step 204, the system evaluates whether avg FER<FERdesired−margina oraverage number (or ath percentile) of HARQtransmission<HARQnumber_desired−marginb. In step 208, the systemevaluates whether avg FER>=FERdesired+margina or average number (or athpercentile) of HARQ transmission>=HARQnumber_desired+marginb. If avgFER>=FERdesired+margina or average number (or ath percentile) of HARQtransmission>=HARQnumber_desired+marginb, the system evaluates whetherthe current MCS level is already the lowest in step 210. If so, thesystem sets PUA=PUA+x dB. This can be done by using CLPC TPC command(absolute or incremental). In this example, x is selected to terminatethe next HARQ transmission one step earlier. Otherwise, the system setsΔSRS=ΔSRS−x dB. In this example, x can be selected so that MCS=MCS−1.The same rule applies to all x's in the following examples.

In step 206, if avg FER<FERdesired−margin1 and the average number (orath percentile) of HARQ transmissions is <HARQnumber_desired−marginb,the system evaluates whether the current MCS level is already thehighest (e.g., 64 QAMS/6) in step 206. If so, the system sets the powerof the UA (PUA)=PUA−x dB. In this example, x can be selected toterminate the next HARQ transmission one step later. Otherwise, thesystem evaluates ΔSRS=ΔSRS+x dB, where x, in one implementation, can beselected so that MCS=MCS+1.

If the current MCS adaptation is appropriate, the system may not changethe MCS value or the UA transmission power. After performing the aboveevaluation, the algorithm repeats for future transmissions.

In a second implementation of the present system illustrated in FIG. 10,at the start of each new transmission a value n is initially set to 1 instep 220 and may be dynamically adjusted based on the UA QoS andperformance requirements (e.g., HARQ termination statistics and FER).Then the system selects an MCS targeting 10% BLER on the nth terminationin step 222, where 1<=n<=maximum number of transmissions.

In the present example, if UA OLPC is based on UA to base station pathloss, the base station may determine the MCS based on the channelquality estimation of the UA to base station link plus an offset. In oneexample, the channel quality estimation of the UA to base station linkmay be performed based on existing Rel-8 mechanisms. In this example,the offset may be the coupling loss difference from the UA to basestation (e.g., CeNB−Crelay). n is initially set to 1 and dynamicallyadjusted based on the UA QoS and performance requirements (e.g., HARQtermination statistics and FER).

Alternatively, if UA OLPC is based on the UA to RN path loss, the basestation may decide the MCS based on the channel quality estimation ofthe UA to RN link. In this case, the RN may need to periodically send UAto RN channel related information, for example, ULSRS and PUSCH SNIR, tothe base station through the wireless backhaul link so that the basestation has knowledge of the UA to RN channel conditions. To savebandwidth on backhaul, channel information reports can be sent in adelta format and are only needed when such delta reaches a certainthreshold.

In step 224, after each UL transmission terminates (e.g., is a successor failure), the base station updates the average number of HARQtransmissions and Frame Erasure Rate (FER). The average can be a windowbased moving average.

In step 226, the system evaluates whether avg FER<FERdesired−margina andthe average number (or ath percentile) of HARQ transmissionHARQnumber_desired−marginb. If so, in step 228 the system evaluateswhether n<maximum number of transmissions. If n<maximum number oftransmissions, the system sets n=n+1. Otherwise, the system setsPUA=PUA−x dB, where x can be selected in order to terminate the nextHARQ transmission one step later.

If step 230, the system evaluates whether avg FER>=FERdesired+margina oraverage number (or ath percentile) of HARQtransmission>=HARQnumber_desired+marginb, the system evaluates n in step232. If so, in step 232, if n>1, the system sets n=n−1. Otherwise, thesystem sets PUA=PUA+x dB, where x may be selected to terminate the nextHARQ transmission one step earlier.

In all other cases, the system maintains the values of n and PUA. Thealgorithm then repeats for future transmission.

In a third implementation of the present system illustrated in FIG. 11,in step 250 the system initially sets a value of A equal to 0.

In step 252 the system selects an MCS. If UA OLPC is based on UA to basestation path loss, the base station may determine the MCS based on thechannel quality estimation of the UA to base station link plus anoffset. The channel quality estimation of the UA to base station linkcan be done based on existing Rel-8 mechanisms. The offset can be thecoupling loss difference between UA and base station (e.g.,CeNB−Crelay). MCSs selected in this way may be denoted as MCS′. As aresult, the actual MCS used is adjusted using MCS=MCS′+A.

Alternatively, in step 252, if UA OLPC is based on the UA to RN pathloss, the base station may determine the MCS based on channel qualityestimation of the UA to RN link. In this example, the RN may need toperiodically send UA to RN channel related information, for example,ULSRS and PUSCH SNIR, to the base station through the wireless backhaullink so that the base station has knowledge of the UA to RN channelconditions. To save bandwidth on backhaul, channel information reportscan be sent in a delta format and may only be needed when such deltareaches a certain threshold. In this example, let MCS selected in thisway be denoted as MCS′. As a result, the actual MCS used is adjustedusing MCS=MCS′+A.

In step 254, after each UL transmission terminates (success or failure),the base station updates the average number (or ath percentile) of HARQtransmissions and average Frame Erasure Rate (FER). The average can be awindow based moving average.

In step 256 the system evaluates whether avg FER<FERdesired−margina orthe average number of HARQ transmission<HARQnumber_desired−marginb. Ifavg FER<FERdesired−margina or average number of HARQ transmissions is<HARQnumber_desired−marginb, in step 258, if the current MCS is alreadythe highest, the system sets PUA=PUA−x dB, where x can be selected todecrease the HARQ termination one step earlier. Otherwise the systemincreases the next new MCS by one level (e.g., A=1).

If step 260 the system evaluates whether avg FER>=FERdesired+margina oraverage number of HARQ transmissions>=HARQnumber_desired+marginb. If avgFER>=FERdesired+margina or average number of HARQtransmission>=HARQnumber_desired+marginb, in step 262, if the currentMCS is already the lowest, the system sets PUA=PUA+x dB, where x can beselected to decrease the HARQ termination one step earlier. Otherwise,the system reduces the next new MCS by one level (e.g., A=−1).

In all other cases, PUA is unchanged and A is set to 0 in step 264.

In a fourth implementation of the present system illustrated in FIG. 12,the system initially selects an MCS in step 280.

In step 280, if UA OLPC is based on UA to base station path loss, thesystem may select an MCS based on channel quality estimation from UL SRSreceived using the UA to base station link (e.g., ULeNB_Q, plus anoffset). The offset can be the coupling loss difference between the UAto base station link and the UA to RN link+ΔSRS (e.g.,CeNB−Crelay+ΔSRS). ΔSRS may be used to compensate the combined channelgain.

Alternatively, in step 280, if UA OLPC is based on the UA to RN pathloss, the system selects MCS based on channel quality estimation from ULSRS received on the UA to RN link (e.g., ULrelay_Q, plus ΔSRS). ΔSRS maybe defined the same way as above.

In step 282, the system is configured to use the current MCS and PUA forthe new transmission. In step 284, after each UL transmission terminates(e.g., with success or failure), the base station updates the averagenumber (or ath percentile) of HARQ transmissions and average FrameErasure Rate (FER). The average can be a window based moving average.

In step 286 the system evaluates whether average FER<FERdesired−marginaand average number of HARQ transmission<HARQnumber_desired−marginb. Ifso, in step 290, if the current MCS is already the highest, the systemsets PUA=PUA−x dB, where x can be selected to decrease the HARQtermination one step earlier. Otherwise, the system sets MCS=MCS+1.

In step 288, the system evaluates whether avg FER>=FERdesired+margina orthe average number of HARQ transmissions>=HARQnumber_desired+marginb. Instep 292, if the current MCS is already the lowest, the system setsPUA=PUA+x dB, where x can be selected to decrease the HARQ terminationone step earlier. Otherwise, the system sets MCS=MCS−1.

In all other cases, MCS and PUA are unchanged. The algorithm thenrepeats for the next new transmissions.

FIG. 13 illustrates the various network entities that participate ininner loop and outer loop link adaptation as described in FIGS. 9-12. InFIG. 13, the first three implementations of the present systemillustrated in FIGS. 9-11 have two loops for link adaptation. Inner loopadaptation 300 is based on uplink channel quality estimation and theadaptation pace is relatively quick. Outer loop adaptation 302 is basedon long term UA QoS measurements and the adaptation pace is slower thaninner loop adaptation 300 to capture the combined channel gain. For thefourth implementation illustrated in FIG. 12, channel quality estimationis only used in the initial MCS selection 304. In that case, MCSadaptation may be based on the long term statistics such as averagenumber of HARQ transmission and average number of FER. Because no innerloop 300 adaptation is used in the fourth proposal, the link adaptationmay not be fast and effective enough to capture the fast fadingvariations. In some cases, proposals one through three (FIGS. 9-11) mayrequire more channel quality estimation feedback, but may lead to betterchannel utilization and better link adaptation stability.

FIG. 14 illustrates a wireless communications system including anembodiment of UA 10. UA 10 is operable for implementing aspects of thedisclosure, but the disclosure should not be limited to theseimplementations. Though illustrated as a mobile phone, the UA 10 maytake various forms including a wireless handset, a pager, a personaldigital assistant (PDA), a portable computer, a tablet computer, alaptop computer. Many suitable devices combine some or all of thesefunctions. In some embodiments of the disclosure, the UA 10 is not ageneral purpose computing device like a portable, laptop or tabletcomputer, but rather is a special-purpose communications device such asa mobile phone, a wireless handset, a pager, a PDA, or atelecommunications device installed in a vehicle. The UA 10 may also bea device, include a device, or be included in a device that has similarcapabilities but that is not transportable, such as a desktop computer,a set-top box, or a network node. The UA 10 may support specializedactivities such as gaming, inventory control, job control, and/or taskmanagement functions, and so on.

The UA 10 includes a display 702. The UA 10 also includes atouch-sensitive surface, a keyboard or other input keys generallyreferred as 704 for input by a user. The keyboard may be a full orreduced alphanumeric keyboard such as QWERTY, Dvorak, AZERTY, andsequential types, or a traditional numeric keypad with alphabet lettersassociated with a telephone keypad. The input keys may include atrackwheel, an exit or escape key, a trackball, and other navigationalor functional keys, which may be inwardly depressed to provide furtherinput function. The UA 10 may present options for the user to select,controls for the user to actuate, and/or cursors or other indicators forthe user to direct.

The UA 10 may further accept data entry from the user, including numbersto dial or various parameter values for configuring the operation of theUA 10. The UA 10 may further execute one or more software or firmwareapplications in response to user commands. These applications mayconfigure the UA 10 to perform various customized functions in responseto user interaction. Additionally, the UA 10 may be programmed and/orconfigured over-the-air, for example from a wireless base station, awireless access point, or a peer UA 10.

Among the various applications executable by the UA 10 are a webbrowser, which enables the display 702 to show a web page. The web pagemay be obtained via wireless communications with a wireless networkaccess node, a cell tower, a peer UA 10, or any other wirelesscommunication network or system 700. The network 700 is coupled to awired network 708, such as the Internet. Via the wireless link and thewired network, the UA 10 has access to information on various servers,such as a server 710. The server 710 may provide content that may beshown on the display 702. Alternately, the UA 10 may access the network700 through a peer UA 10 acting as an intermediary, in a relay type orhop type of connection.

FIG. 15 shows a block diagram of the UA 10. While a variety of knowncomponents of UAs 110 are depicted, in an embodiment a subset of thelisted components and/or additional components not listed may beincluded in the UA 10. The UA 10 includes a digital signal processor(DSP) 802 and a memory 804. As shown, the UA 10 may further include anantenna and front end unit 806, a radio frequency (RF) transceiver 808,an analog baseband processing unit 810, a microphone 812, an earpiecespeaker 814, a headset port 816, an input/output interface 818, aremovable memory card 820, a universal serial bus (USB) port 822, ashort range wireless communication sub-system 824, an alert 826, akeypad 828, a liquid crystal display (LCD), which may include a touchsensitive surface 830, an LCD controller 832, a charge-coupled device(CCD) camera 834, a camera controller 836, and a global positioningsystem (GPS) sensor 838. In an embodiment, the UA 10 may include anotherkind of display that does not provide a touch sensitive screen. In anembodiment, the DSP 802 may communicate directly with the memory 804without passing through the input/output interface 818.

The DSP 802 or some other form of controller or central processing unitoperates to control the various components of the UA 10 in accordancewith embedded software or firmware stored in memory 804 or stored inmemory contained within the DSP 802 itself. In addition to the embeddedsoftware or firmware, the DSP 802 may execute other applications storedin the memory 804 or made available via information carrier media suchas portable data storage media like the removable memory card 820 or viawired or wireless network communications. The application software maycomprise a compiled set of machine-readable instructions that configurethe DSP 802 to provide the desired functionality, or the applicationsoftware may be high-level software instructions to be processed by aninterpreter or compiler to indirectly configure the DSP 802.

The antenna and front end unit 806 may be provided to convert betweenwireless signals and electrical signals, enabling the UA 10 to send andreceive information from a cellular network or some other availablewireless communications network or from a peer UA 10. In an embodiment,the antenna and front end unit 806 may include multiple antennas tosupport beam forming and/or multiple input multiple output (MIMO)operations. As is known to those skilled in the art, MIMO operations mayprovide spatial diversity which can be used to overcome difficultchannel conditions and/or increase channel throughput. The antenna andfront end unit 806 may include antenna tuning and/or impedance matchingcomponents, RF power amplifiers, and/or low noise amplifiers.

The RF transceiver 808 provides frequency shifting, converting receivedRF signals to baseband and converting baseband transmit signals to RF.In some descriptions a radio transceiver or RF transceiver may beunderstood to include other signal processing functionality such asmodulation/demodulation, coding/decoding, interleaving/deinterleaving,spreading/despreading, inverse fast Fourier transforming (IFFT)/fastFourier transforming (FFT), cyclic prefix appending/removal, and othersignal processing functions. For the purposes of clarity, thedescription here separates the description of this signal processingfrom the RF and/or radio stage and conceptually allocates that signalprocessing to the analog baseband processing unit 810 and/or the DSP 802or other central processing unit. In some embodiments, the RFTransceiver 808, portions of the Antenna and Front End 806, and theanalog base band processing unit 810 may be combined in one or moreprocessing units and/or application specific integrated circuits(ASICs).

The analog base band processing unit 810 may provide various analogprocessing of inputs and outputs, for example analog processing ofinputs from the microphone 812 and the headset 816 and outputs to theearpiece 814 and the headset 816. To that end, the analog base bandprocessing unit 810 may have ports for connecting to the built-inmicrophone 812 and the earpiece speaker 814 that enable the UA 10 to beused as a cell phone. The analog base band processing unit 810 mayfurther include a port for connecting to a headset or other hands-freemicrophone and speaker configuration. The analog base band processingunit 810 may provide digital-to-analog conversion in one signaldirection and analog-to-digital conversion in the opposing signaldirection. In some embodiments, at least some of the functionality ofthe analog base band processing unit 810 may be provided by digitalprocessing components, for example by the DSP 802 or by other centralprocessing units.

The DSP 802 may perform modulation/demodulation, coding/decoding,interleaving/deinterleaving, spreading/despreading, inverse fast Fouriertransforming (IFFT)/fast Fourier transforming (FFT), cyclic prefixappending/removal, and other signal processing functions associated withwireless communications. In an embodiment, for example in a codedivision multiple access (CDMA) technology application, for atransmitter function the DSP 802 may perform modulation, coding,interleaving, and spreading, and for a receiver function the DSP 802 mayperform despreading, deinterleaving, decoding, and demodulation. Inanother embodiment, for example in an orthogonal frequency divisionmultiplex access (OFDMA) technology application, for the transmitterfunction the DSP 802 may perform modulation, coding, interleaving,inverse fast Fourier transforming, and cyclic prefix appending, and fora receiver function the DSP 802 may perform cyclic prefix removal, fastFourier transforming, deinterleaving, decoding, and demodulation. Inother wireless technology applications, yet other signal processingfunctions and combinations of signal processing functions may beperformed by the DSP 802.

The DSP 802 may communicate with a wireless network via the analogbaseband processing unit 810. In some embodiments, the communication mayprovide Internet connectivity, enabling a user to gain access to contenton the Internet and to send and receive e-mail or text messages. Theinput/output interface 818 interconnects the DSP 802 and variousmemories and interfaces. The memory 804 and the removable memory card820 may provide software and data to configure the operation of the DSP802. Among the interfaces may be the USB interface 822 and the shortrange wireless communication sub-system 824. The USB interface 822 maybe used to charge the UA 10 and may also enable the UA 10 to function asa peripheral device to exchange information with a personal computer orother computer system. The short range wireless communication sub-system824 may include an infrared port, a Bluetooth interface, an IEEE 802.11compliant wireless interface, or any other short range wirelesscommunication sub-system, which may enable the UA 10 to communicatewirelessly with other nearby mobile devices and/or wireless basestations.

The input/output interface 818 may further connect the DSP 802 to thealert 826 that, when triggered, causes the UA 10 to provide a notice tothe user, for example, by ringing, playing a melody, or vibrating. Thealert 826 may serve as a mechanism for alerting the user to any ofvarious events such as an incoming call, a new text message, and anappointment reminder by silently vibrating, or by playing a specificpre-assigned melody for a particular caller.

The keypad 828 couples to the DSP 802 via the interface 818 to provideone mechanism for the user to make selections, enter information, andotherwise provide input to the UA 10. The keyboard 828 may be a full orreduced alphanumeric keyboard such as QWERTY, Dvorak, AZERTY andsequential types, or a traditional numeric keypad with alphabet lettersassociated with a telephone keypad. The input keys may include atrackwheel, an exit or escape key, a trackball, and other navigationalor functional keys, which may be inwardly depressed to provide furtherinput function. Another input mechanism may be the LCD 830, which mayinclude touch screen capability and also display text and/or graphics tothe user. The LCD controller 832 couples the DSP 802 to the LCD 830.

The CCD camera 834, if equipped, enables the UA 10 to take digitalpictures. The DSP 802 communicates with the CCD camera 834 via thecamera controller 836. In another embodiment, a camera operatingaccording to a technology other than Charge Coupled Device cameras maybe employed. The GPS sensor 838 is coupled to the DSP 802 to decodeglobal positioning system signals, thereby enabling the UA 10 todetermine its position. Various other peripherals may also be includedto provide additional functions, e.g., radio and television reception.

FIG. 16 illustrates a software environment 902 that may be implementedby the DSP 802. The DSP 802 executes operating system drivers 904 thatprovide a platform from which the rest of the software operates. Theoperating system drivers 904 provide drivers for the UA hardware withstandardized interfaces that are accessible to application software. Theoperating system drivers 904 include application management services(AMS) 906 that transfer control between applications running on the UA10. Also shown in FIG. 16 are a web browser application 908, a mediaplayer application 910, and Java applets 912. The web browserapplication 908 configures the UA 10 to operate as a web browser,allowing a user to enter information into forms and select links toretrieve and view web pages. The media player application 910 configuresthe UA 10 to retrieve and play audio or audiovisual media. The Javaapplets 912 configure the UA 10 to provide games, utilities, and otherfunctionality. A component 914 might provide functionality describedherein.

The UA 10, base station 120, and other components described above mightinclude a processing component that is capable of executing instructionsrelated to the actions described above. FIG. 17 illustrates an exampleof a system 1000 that includes a processing component 1010 suitable forimplementing one or more embodiments disclosed herein. In addition tothe processor 1010 (which may be referred to as a central processor unit(CPU or DSP), the system 1000 might include network connectivity devices1020, random access memory (RAM) 1030, read only memory (ROM) 1040,secondary storage 1050, and input/output (I/O) devices 1060. In somecases, some of these components may not be present or may be combined invarious combinations with one another or with other components notshown. These components might be located in a single physical entity orin more than one physical entity. Any actions described herein as beingtaken by the processor 1010 might be taken by the processor 1010 aloneor by the processor 1010 in conjunction with one or more componentsshown or not shown in the drawing.

The processor 1010 executes instructions, codes, computer programs, orscripts that it might access from the network connectivity devices 1020,RAM 1030, ROM 1040, or secondary storage 1050 (which might includevarious disk-based systems such as hard disk, floppy disk, or opticaldisk). While only one processor 1010 is shown, multiple processors maybe present. Thus, while instructions may be discussed as being executedby a processor, the instructions may be executed simultaneously,serially, or otherwise by one or multiple processors. The processor 1010may be implemented as one or more CPU chips.

The network connectivity devices 1020 may take the form of modems, modembanks, Ethernet devices, universal serial bus (USB) interface devices,serial interfaces, token ring devices, fiber distributed data interface(FDDI) devices, wireless local area network (WLAN) devices, radiotransceiver devices such as code division multiple access (CDMA)devices, global system for mobile communications (GSM) radio transceiverdevices, worldwide interoperability for microwave access (WiMAX)devices, and/or other well-known devices for connecting to networks.These network connectivity devices 1020 may enable the processor 1010 tocommunicate with the Internet or one or more telecommunications networksor other networks from which the processor 1010 might receiveinformation or to which the processor 1010 might output information.

The network connectivity devices 1020 might also include one or moretransceiver components 1025 capable of transmitting and/or receivingdata wirelessly in the form of electromagnetic waves, such as radiofrequency signals or microwave frequency signals. Alternatively, thedata may propagate in or on the surface of electrical conductors, incoaxial cables, in waveguides, in optical media such as optical fiber,or in other media. The transceiver component 1025 might include separatereceiving and transmitting units or a single transceiver. Informationtransmitted or received by the transceiver 1025 may include data thathas been processed by the processor 1010 or instructions that are to beexecuted by processor 1010. Such information may be received from andoutputted to a network in the form, for example, of a computer databaseband signal or signal embodied in a carrier wave. The data may beordered according to different sequences as may be desirable for eitherprocessing or generating the data or transmitting or receiving the data.The baseband signal, the signal embedded in the carrier wave, or othertypes of signals currently used or hereafter developed may be referredto as the transmission medium and may be generated according to severalmethods well known to one skilled in the art.

The RAM 1030 might be used to store volatile data and perhaps to storeinstructions that are executed by the processor 1010. The ROM 1040 is anon-volatile memory device that typically has a smaller memory capacitythan the memory capacity of the secondary storage 1050. ROM 1040 mightbe used to store instructions and perhaps data that are read duringexecution of the instructions. Access to both RAM 1030 and ROM 1040 istypically faster than to secondary storage 1050. The secondary storage1050 is typically comprised of one or more disk drives or tape drivesand might be used for non-volatile storage of data or as an over-flowdata storage device if RAM 1030 is not large enough to hold all workingdata. Secondary storage 1050 may be used to store programs that areloaded into RAM 1030 when such programs are selected for execution.

The I/O devices 1060 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls,voice recognizers, card readers, paper tape readers, printers, videomonitors, or other well-known input/output devices. Also, thetransceiver 1025 might be considered to be a component of the I/Odevices 1060 instead of or in addition to being a component of thenetwork connectivity devices 1020. Some or all of the I/O devices 1060may be substantially similar to various components depicted in thepreviously described drawing of the UA 10, such as the display 702 andthe input 704.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and may be made without departing from the spirit and scopedisclosed herein.

To apprise the public of the scope of this invention, the followingclaims are made:
 1. A method for determining a Modulation and CodingScheme (MCS) for a wireless communication system, the method including:identifying an MCS for communications between a user agent (UA) and atleast one of a base station and a relay node (RN); selecting the MCSbased at least upon a coupling loss of a first link between the UA andthe base station and/or a coupling loss of a second link between the UAand the RN; allocating an uplink (UL) resource for communication fromthe UA to the RN when a coupling loss of UL communication on the firstlink is greater than a coupling loss of UL communication on the secondlink; and allocating a downlink (DL) resource for communication from thebase station to the UA when a power level of DL communication on thesecond link is less than a power level of DL communication on the firstlink.
 2. The method of claim 1, further comprising determining an errorrate of a communication channel between the UA and at least one of thebase station and the RN, wherein the MCS is further selected based uponthe error rate and a coupling loss difference between the first link andthe second link.
 3. The method of claim 1, further comprisingdetermining an error rate of a communication channel between the UA andat least one of the base station and the RN, wherein the error rate isdetermined based upon at least one of a number of Hybrid AutomaticRepeat reQuest (HARQ) transmissions on the communication channel or aFrame Erasure Rate (FER) on the communication channel.
 4. The method ofclaim 3, further comprising selecting a lowest MCS level as the MCS if:an average number of HARQ transmissions on the communication channel isgreater than or equal to a desired number of HARQ transmissions on thecommunication channel; or an average FER on the communication channel isgreater than or equal to a desired FER.
 5. The method of claim 3,further comprising increasing the MCS by one level if: an average numberof HARQ transmissions on the communication channel is less than adesired number of HARQ transmissions on the communication channel; or anaverage FER on the communication channel is less than a desired FER. 6.The method of claim 3, further comprising selecting a highest MCS levelas the MCS if: an FER on the communication channel is less than adesired FER; and an average number of HARQ transmissions on thecommunication channel is less than a desired number of HARQtransmissions on the communication channel.
 7. The method of claim 3,further comprising: increasing the MCS and/or reducing a transmissionpower of the UA when the error rate is below a first threshold; anddecreasing the MCS and/or increasing a transmission power of the UA whenthe error rate is above a second threshold.
 8. A base station fordetermining a Modulation and Coding Scheme (MCS) for a wirelesscommunication system, the base station comprising: a processor, theprocessor being configured to: select an MCS for communications betweena user agent (UA) and at least one of a base station and a relay node(RN), wherein the MCS is selected based at least upon a coupling loss ofa first link between the UA and the base station and/or a coupling lossof a second link between the UA and the RN; allocate an uplink (UL)resource for communication from the UA to the RN when a coupling loss ofUL communication on the first link is greater than a coupling loss of ULcommunication on the second link; and allocate a downlink (DL) resourcefor communication from the base station to the UA when a power level ofDL communication on the second link is less than a power level of DLcommunication on the first link.
 9. The base station of claim 8, whereinthe processor is further configured to: determine an error rate of acommunication channel between the UA and at least one of the basestation and the RN; and select the MCS based upon the error rate and acoupling loss difference between the first link and the second link. 10.The base station of claim 8, wherein the processor is configured todetermine an error rate a communication channel between the UA and atleast one of the base station and the RN, wherein the error rate isdetermined based at least upon one of a number of Hybrid AutomaticRepeat reQuest (HARQ) transmissions on the communication channel or aFrame Erasure Rate (FER) on the communication channel.
 11. The basestation of claim 10, wherein the processor is further configured toselect a lowest MCS level as the MCS if: an average number of HARQtransmissions on the communication channel is greater than or equal to adesired number of HARQ transmissions on the communication channel; or anaverage FER on the communication channel is greater than or equal to adesired FER.
 12. The base station of claim 10, wherein the processor isfurther configured to increase the MCS by one level if: an averagenumber of HARQ transmissions on the communication channel is less than adesired number of HARQ transmissions on the communication channel; or anaverage FER on the communication channel is less than a desired FER. 13.The base station of claim 10, wherein the processor is furtherconfigured to select a highest MCS level as the MCS if: an average FERon the communication channel is less than a desired FER; and an averagenumber of HARQ transmissions on the communication channel is less than adesired number of HARQ transmissions on the communication channel. 14.The base station of claim 10, wherein the processor is furtherconfigured to: increase the MCS and/or reduce a transmission power ofthe UA when the error rate is below a first threshold; and decrease theMCS and/or increase a transmission power of the UA when the error rateis above a second threshold.
 15. A wireless communication system,comprising: a user agent (UA) for communicating with a base station anda relay node (RN), the UA being configured to receive an instructionfrom the base station, the instruction specifying a Modulation andCoding Scheme (MCS); and a base station configured to: allocate anuplink (UL) resource for communication from the UA to the RN when acoupling loss of a first UL channel between the UA and the base stationis greater than a coupling loss of a second UL channel between the UAand the RN; and allocate a downlink (DL) resource for communication fromthe base station to the UA when a power level of a first DL channelbetween the UA and the RN is less than a power level of a second DLchannel between the base station and the UA.
 16. The wirelesscommunication system of claim 15, wherein the base station is configuredto select the MCS using at least one of: a signal quality value of acommunication channel between the UA and the base station; a couplingloss difference between the first and second UL channels; or a couplingloss difference between the first and second DL channels.
 17. Thewireless communication system of claim 15, wherein the base station isfurther configured to select the MCS based at least upon an error rateof a communication channel between the UA and the base station, whereinthe error rate is based at least upon one of the number of HybridAutomatic Repeat reQuest (HARQ) transmissions on the communicationchannel or a Frame Erasure Rate (FER) on the communication channel. 18.The wireless communication system of claim 17, wherein the base stationis further configured to select a lowest MCS level as the MCS if: anaverage number of HARQ transmissions on the communication channel isgreater than or equal to a desired number of HARQ transmissions on thecommunication channel; or an average FER on the communication channel isgreater than or equal to a desired FER.
 19. The wireless communicationsystem of claim 17, wherein the base station is further configured toincrease the MCS by one level if: an average number of HARQtransmissions on the communication channel is less than a desired numberof HARQ transmissions on the communication channel; or an average FER onthe communication channel is less than a desired FER.
 20. The wirelesscommunication system of claim 17, wherein the base station is furtherconfigured to select a highest MCS level as the MCS if: an average FERon the communication channel is less than a desired FER; and an averagenumber of HARQ transmissions on the communication channel is less than adesired number of HARQ transmissions on the communication channel.